OBJECTIVE: The present study was aimed at evaluating the practical peak voltage (PPV) determined from the voltage waveform applied to x-ray tubes and comparing it with some kVp definitions for different types of x-ray equipment: single-phase (full-wave) and three-phase (six-pulse) clinical x-ray generators, and an industrial constant potential apparatus. MATERIALS AND METHODS: The study involved the comparison between invasively measured PPV (with voltage dividers) and values obtained with two commercial noninvasive meters, besides values of other quantities utilized for measuring the x-ray tube peak voltage. The PPV variation with the voltage ripple was also analyzed in the present study. RESULTS: The authors observed that the difference between PPV and the most common peak voltage definitions increases with the ripple. PPV values varied up to 3% and 5%, respectively, in the comparison between invasive and non-invasive measurements with single-phase and three-phase devices. CONCLUSION: The results demonstrated that voltage ripple is the main quantity influencing the invasive or non-invasive PPV determination. Additionally, non-invasively measured PPV values should be evaluated taking into consideration their dependence on the data sample rate and waveform obtained by the device.

Keywords: Practical peak voltage, X-ray tubes, Voltage divider, Voltage waveform, Peak voltage, kVp meters

OBJECTIVE: To develop an acceptance testing protocol for magnetic resonance imaging systems and to show which and how phantoms could be used to collect data. MATERIALS AND METHODS: The definition, procedure, analysis and the acceptation criteria were created for each of 15 selected tests. RESULTS: These tests allow the evaluation of technical specifications stated on the manufacturer's sales proposal and to establish reference values to be used in subsequent constancy tests. CONCLUSION: Future quality assurance programs in magnetic resonance imaging should consider employing tests similar or equal to the ones described in this paper.

Keywords: Magnetic resonance imaging, Quality control

OBJECTIVE: The authors have sought to study the calibration of a clinical P_KA meter (Diamentor E2) and a calibrator for clinical meters (PDC) in the Laboratory of Ionizing Radiation Metrology at Instituto de Energia e Ambiente - Universidade de São Paulo. MATERIALS AND METHODS: Different qualities of both incident and transmitted beams were utilized in conditions similar to a clinical setting, analyzing the influence from the reference dosimeter, from the distance between meters, from the filtration and from the average beam energy. Calibrations were performed directly against a standard 30 cm³ cylindrical chamber or a parallel-plate monitor chamber, and indirectly against the PDC meter. RESULTS: The lowest energy dependence was observed for transmitted beams. The cross calibration between the Diamentor E2 and the PDC meters, and the PDC presented the greatest propagation of uncertainties. CONCLUSION: The calibration coefficient of the PDC meter showed to be more stable with voltage, while the Diamentor E2 calibration coefficient was more variable. On the other hand, the PDC meter presented greater uncertainty in readings (5.0%) than with the use of the monitor chamber (3.5%) as a reference.

Keywords: Kerma; Meters; Calibration; Dosimetry; Radiology; X-rays.